1. Field of the Invention
The present invention relates to a lamp socket into which a lamp plug is designed to fit, for example, a lamp socket for mounting a lamp such as a high-intensity discharge lamp to be used as a headlight on the front of an automobile or another vehicle.
2. Description of the Related Art
Recent years, lighting devices to be used as headlights of automobiles and so on have been shifted from halogen lamp systems to high-intensity discharge (HID) lamp systems because of their advantages with respect to large light pencils, excellent lamp efficiencies, and long lasting qualities. The typical lighting device of the HID lamp system mainly comprises a discharge lamp bulb which is removably attached to a lamp plug, an igniter that allows the instantaneous generation of high-voltage discharge, and a ballast for controlling the operation of the igniter. The HID lamp system further comprises a lamp socket in which the lamp plug of the lighting device can be removably plugged. The lamp socket mainly comprises a high-voltage side terminal, a low-voltage side terminal, and. an insulation seal member. In the lamp socket, the insulation seal member is arranged between the high-voltage side terminal and the low-voltage side terminal for providing a perfect electrical insulation between them because a high voltage (e.g., 30 KV) generated by the igniter is momentarily applied to the discharge lamp.
Concretely, the conventional lamp socket is constructed as follows. That is, the high-voltage side terminal is positioned at a center of the lamp socket so that it electrically contacts to a high-voltage side terminal of the lamp plug. On the other hand, the low-voltage side terminal is located in the proximity of a peripheral portion of the lamp socket so that it electrically contacts to a low-voltage side terminal of the lamp plug. In addition, the insulation seal member is arranged between the high-voltage side terminal and the low-voltage side terminal in order to completely electrically isolate these components. Therefore, both insulation and withstand voltage properties of the boundary between the high-voltage side terminal and the low-voltage side terminal of the lamp socket are enhanced in order to support a high voltage applied to the lamp plug.
In the lamp socket having the structure described above, an insulation seal member is fixed on the lamp socket only by sliding the insulation seal member onto the outside of a tubular guide portion that surrounds the high-voltage side terminal. If the lamp plug is pulled out of the lamp socket for replacing a lamp bulb with new one, the position of the insulation seal member may be left near the lamp plug so that it may be removed from the lamp socket as the lamp plug is pulled out of the lamp socket. Thus, a new lamp may be fitted into the lamp socket without realizing that the insulation seal member has been removed. This results in an insufficient electrical insulation between the high-voltage side terminal and low-voltage side terminal. Such an insufficient electrical insulation causes serious damage to a lighting mechanism or the like.
For solving such a disadvantage, for example, the Japanese Patent Laying-open No. 10-64643 (1998) discloses a lamp socket with an additional structural component for preventing the insulation seal member from dislodging when the lamp plug is pulled out of the lamp socket.
FIG. 10 is a cross sectional view of the conventional lamp socket disclosed in the Japanese Patent Laying-open No. 10-64643 (1998).
In the figure, the reference numeral 1 denotes a lamp such as a HID lamp bulb, 2 denotes a lamp plug having a low-voltage side terminal 3 in the shape of a cylinder and a high-voltage side terminal 4 arranged in the center of the lamp plug 2. The reference numeral 5 denotes a lamp socket into which the lamp plug 2 can be removably plugged, 6 denotes a tubular guide portion which is integrally molded in the inside of the lamp socket 5, and 7 denotes a high-voltage side terminal. The high-voltage side terminal 7 is fixed in place by guiding it along the inner peripheral surface of the tubular guide portion 6 and inserting one end portion of the terminal 7 through an a slit formed on the bottom of the lamp socket 5. Thus, the high-voltage side terminal 7 is positioned in the tubular guide portion 6 so that it is able to make an electrical contact with a high-voltage side terminal 4 of the lamp plug 2 as shown in the figure. Furthermore, the reference numeral 8 denotes a low-voltage side terminal which is fixed in place by inserting one end portion of the terminal 8 through a predetermined place between an inner peripheral surface of the lamp socket 5 and an outer peripheral surface of the guide portion 6. Such a low-voltage side terminal 8 is able to make electrical contact with a low-voltage side terminal 3 of the lamp plug 2 as shown in the figure. The reference numeral 9 denotes a tubular insulation seal member which is placed over the outer peripheral surface of the tubular guide portion 6 to provide electrical isolation between the high-voltage side (i.e., terminals 4, 7) and the low-voltage side (i.e., terminals 3, 8). The reference numeral 10 denotes a tubular stopper having a flanged portion 10a horizontally extended outward from its one end. As shown in the figure, the flanged portion 10a is provided as a press plate for pressing down the insulation seal member 9 in the direction of fitting the insulation seal member 9 onto the guide portion 6.
In other words, the insulation seal member 9 can be fixed on the conventional lamp socket as follows for preventing the removal of the insulation seal member 9 from the guide portion 6.
Firstly the insulation seal member 9 is fitted onto the outer periphery of the tubular guide portion 6 of the lamp socket 5. Then, the tubular stopper 10 is inserted into the inside of the tubular guide portion 6 to fit it in place. Simultaneously, the press plate 10a of the stopper 10 comes into press-contact with an upper end of the guide portion 6 that extends toward the lamp plug 2 from the bottom of the lamp socket 5. Consequently, the insulation seal member 6 is prevented from detaching from the tubular guide portion 6.
As the conventional lamp socket is constructed as described above, the stopper 10 must be provided as an additional member for preventing the detachment of the insulation seal member 9. Therefore, the number of the structural components of the lamp socket 5 is increased to that extent and the structural complexity of the lamp socket 5 is increased. Thus the manufacturing cost of such a lamp socket 5 rises.
Moreover, the insulation seal member 9 is generally prepared by molding a silicon rubber, in order to obtain sufficient flexibility to adhere to the boundary between the inner peripheral surface of the lamp plug 2 and the outer peripheral surface of the insulation seal member 9. If the lamp plug 2 is pulled out of the lamp socket 5 to replace a bulb 1 with new one or the like, the stopper 10 prevents the detachment of the insulation seal member 9. However, the insulation seal member 9 may be partially curled up or peeled off because of its excellent flexibility and poor tearing strength. Therefore, it is very difficult to keep the normal insulation performance or the like if the insulation seal member 9 is deformed.